lkml.org 
[lkml]   [2022]   [Nov]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH] powerpc/bpf: Only update ldimm64 during extra pass when it is an address
Date


Le 24/11/2022 à 11:13, Naveen N. Rao a écrit :
> Christophe Leroy wrote:
>> ldimm64 is not only used for loading function addresses, and
>
> That's probably true today, but I worry that that can change upstream
> and we may not notice at all.

Not sure what you mean.

Today POWERPC considers that ldimm64 is _always_ loading a function
address whereas upstream BPF considers that ldimm64 is a function only
when it is flagged BPF_PSEUDO_FUNC.

In what direction could that change in the future ?

For me if they change that it becomes an API change.

Christophe


>
>> the NOPs added for padding are impacting performance, so avoid
>> them when not necessary.
>>
>> On QEMU mac99, with the patch:
>>
>> test_bpf: #829 ALU64_MOV_K: all immediate value magnitudes jited:1
>> 167436810 PASS
>> test_bpf: #831 ALU64_OR_K: all immediate value magnitudes jited:1
>> 170702940 PASS
>>
>> Without the patch:
>>
>> test_bpf: #829 ALU64_MOV_K: all immediate value magnitudes jited:1
>> 173012360 PASS
>> test_bpf: #831 ALU64_OR_K: all immediate value magnitudes jited:1
>> 176424090 PASS
>>
>> That's a 3.5% performance improvement.
>
> A better approach would be to do a full JIT during the extra pass.
> That's what most other architectures do today. And, as long as we can
> ensure that the JIT'ed program size can never increase during the extra
> pass, we should be ok to do a single extra pass.
>
>
> - Naveen
\
 
 \ /
  Last update: 2022-11-24 13:25    [W:0.067 / U:0.748 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site